As shown in FIG. 2, a typically prior art wireless packet 200 includes of a synchronization header (SHR) 210, a physical layer header (PHR) 220, and a payload 230 of data. The SHR 210 contains a preamble 240 and start of frame delimiter (SFD) 250.
The SHR is used to achieve signal acquisition, signal synchronization and ranging. The SFD 250 is used to detect the end of the preamble 240, the end of the SHR header 210, and the start of the PHR 220. That is, the SFD 250 serves as a delimiter between the SHR and the PHR.
The Task Group for the emerging IEEE 802.15.4a standard for an alternative physical layer is standardizing the structure of the preamble 240 and the SFD 250. According to the IEEE Draft P802.15.4a/D2, April, 2006, incorporated herein by reference, the preamble 240 has a repetition of eight identical, fixed length perfectly balanced ternary sequences (PBTS) 110 of ternary symbols (Si), as shown in FIG. 1, i.e., all X are the same.
As shown in FIG. 3, the ternary symbols (Si) 110 can be a pulse with positive (+) polarity 320, a pulse with negative (−) polarity 330, or a pulse with a zero (0) multiplier 340. Each pulse is separated from the next by a pulse repetition interval (PRI) 310. The PBTS 110 in FIG. 3 have perfect periodic autocorrelation properties in a sense that side lobes around an autocorrelation peak are zero as shown in FIG. 3 for symbols S1.
FIG. 2 shows the SFD 250 specified in the IEEE Draft P802.15.4a/D2 standard. The SFD also has a periodic structure that includes a repetition of the identical base pattern X 260. The repetition of the base pattern X 260 within the SFD 250 generates periodicity. The periodicity helps to achieve statistical multiplexing gain from the repetitions.
However, the SFD should have an arbitrary, non-periodic pattern to help the receiver to determine what section of the SFD 250 is being received. Therefore, it is desired to improve the SFD by removing the periodicity without sacrificing the statistical multiplexing gain that is achieved by repetitions of the base pattern X.